Analyzing the effect of prenatal care on pregnancy outcome: a conditional approach

We used vital statistics data to examine the effect of the time of entry into prenatal care relative to the gestational age of delivery on pregnancy outcome. Early entry into prenatal care was associated with better outcomes only in women who delivered at 37 through 42 weeks of gestation. We are concerned that the evaluation of the effect of prenatal care using vital statistics data may be questionable because of the problems inherent in the data.